1. Field of the Invention
The present invention relates to a moving picture experts group (MPEG) system, and more particularly, to a transport stream (TS) encoder for encoding an elementary stream in units of fields in the MPEG-2 and a method therefor. The present application is based on Korean Patent Application No. 99,42309, filed Oct. 1, 1999, which is incorporated herein by reference.
2. Description of the Related Art
The MPEG-2 system specifies the syntax of MPEG audio and video streams. The MPEG system has two types of methods. One, which is referred to as a program stream (PS), is for constructing a program. The other, which is referred to as a transport stream (TS), is for constructing a plurality of programs.
A multiplexing method by a packet is adopted in the MPEG system. Namely, the MPEG system segments a video/audio elementary stream (ES) into a bit stream in units of packets and multiplexes the video/audio elementary stream along with additional information such as a header. At this time, information of distinguishing a video packet from an audio packet is included in the header. The length of the packet is set to be 216 (64 KB) in the MPEG system in order to be suitable for various applications. For flexibility, each packet can have a fixed length or a variable length. Information on the length of the packet is included in the header.
In the PS method, a plurality of packets (referred to as a packetized elementary stream (PES) in the MPEG-2) are grouped to construct a pack. In the TS method, a PES is re-segmented and a plurality of transport stream (TS) packets having a relatively short length are constituted. At this time, the length of a TS packet is 188 bytes and each TS packet is divided into four ATM cells and then transmitted.
A header of four bytes exists in the TS packet. A packet ID (PID) which identifies the packet exists in the header. The PID is written in a program management table (PMT) of program specific information (PSI). The TS packet whose PID is “0” is used for transmitting the PSI.
Information on programs to which each of the TS packets belongs is required since the TS transmits a plurality of programs. This information is referred to as the PSI. The PSI is transmitted by the TS packet having a designated ID and a packet designated by a primitive PSI. The PSI packet consists of a PAT, a PMT, and a conditional access table (CAT). The PSI information is transmitted at least once within 0.7 seconds.
The PAT records information on a program and includes the PID of the packet including the PMT.
A continuity counter for examining the continuity of packets having the same PID is included in the header.
The TS encoder re-segments the PES packet and constructs the TS packet. The length of the PES packet is not fixed and the PES packet includes 16 bit header information so that the length thereof can be shown.
In conventional technology, the TS packet is formed by multiplexing a plurality of programs. Accordingly, when one program is multiplexed, hardware becomes complicated. Also, when the TS packet is constituted in units of frames, it is not possible to desirably edit or re-construct the TS packet. This is because it is difficult to re-construct information on a desired frame since the PSI information exists once every 0.7 seconds.